The present invention discloses an improved drum brake shoe adjuster.
1. Field of the Invention
This invention relates to drum brakes, and more specifically to an improved drum brake shoe adjusting device. The preferred embodiment of the disclosed invention is a floating adjuster with a single adjusting rod. One specifically disclosed embodiment shows an adjuster with an adjusting rod, forming a plunger or piston, in a cylinder, and driven by grease forced into the cylinder by a grease gun through a zerk grease fitting. Another specifically disclosed embodiment shows a mechanical adjuster with a rod, forming a rack, driven by a pinion gear.
2. Discussion of Prior Art
Screw-type devices for adjusting drum brake shoe clearance to accommodate brake shoe material wear are well-known in the prior art. These devices are used to adjust the clearance between the brake shoes, which carry the brake material, and the brake drum, in order to account for wearing of the brake material. In most prior art devices, the adjuster increases the distance between the ends of two shoes, thereby forcing the shoe pads into tighter clearance with the drum. In one very common prior art arrangement, manual adjustment is accomplished by inserting a brake spoon, screwdriver, or similar tool through a slot in the brake""s back plate to reach a star wheel, which, when rotated, turns a threaded adjuster screw and changes the distance between the brake shoes and the drum.
However, these screw-type adjuster assemblies are often difficult to use, time-consuming, and can be dangerous as well. Problems with the screw adjusters typically arise because the back plate is too close to the vehicle""s springs or frame to allow adequate room for operation of the brake spoon. For example, with many vehicles and trailers, the space between the backing plate and the leaf spring is so narrow that it is extremely difficult to insert the brake spoon through the slot in the brake back plate in order to engage and rotate the star wheel. Moreover, the mechanical adjuster parts are exposed to significant heat generated from the brake as well as to corrosive elements, such as rain, grit, road salt, and salt water, so that the parts rust and fuse. In the case of boat trailers, the drum brakes are often entirely submerged in water when the boat is launched or retrieved. Corrosion is a problem with many conventional adjusters especially because the parts are small and delicate in order to fit within the brake. If the star wheel has seized or frozen due to rust, dirt, or corrosion, the drum brake assembly must be completely removed in order to release or replace the adjuster. Thus, manually adjusting brakes using the screw-type adjusters can be time consuming and frustrating.
Moreover, conventional adjusters are also dangerous, because the vehicle on which the brakes require adjustment must be jacked up off the ground to allow for free rotation of the vehicle wheels to test the brake adjustment. With conventional adjusters, the person doing the brake adjustment must lie on the ground or stand under the jacked-up vehicle in order to operate the adjuster, which can only be reached from the inside of the wheel; that is, from under the vehicle or trailer. Thus, conventional drum brake adjustment is awkward and dangerous.
It is one object of the present invention to provide a brake shoe adjuster that will resist corrosion and seizing. It is another object of the present invention to provide a brake shoe adjuster that is protected against rust, dirt, water, corrosion, or other contamination. It is another object of the present invention to provide a brake shoe adjuster that is a sealed unit. It is another object of the present invention to provide a brake shoe adjuster that is safe to use. It is another object of the present invention to provide a brake shoe adjuster that can be used by a person standing next to the vehicle or trailer wheel rather than under it. It is another object of the present invention to provide a brake shoe adjuster that is easy, fast, and inexpensive to use.
In accordance with these objectives, the present invention provides a floating brake shoe adjuster that uses a single rod, in a sealed unit. In one preferred embodiment, an hydraulic adjuster comprises a cylinder housing, a chamber, a plunger or piston, a grease fitting, and a slotted adjusting ram connected to the piston which travels according to the amount of grease pumped into the chamber through the grease fitting. The slotted adjusting ram straddles a saddle at one end of a brake shoe. Another slotted ram at the opposite end of the cylinder housing rides against a saddle at the end of the other shoe. The adjuster is not fixed to the back plate, but is allowed to float. A grease gun is used to pump grease into the chamber through the grease fitting. The grease pumped into the chamber forces the piston out, thereby driving out the shoes against the drum. Because the adjuster floats, the shoes will center themselves, allowing a consistent clearance between the shoes and the drum. The grease fitting, often referred to as a xe2x80x9czerkxe2x80x9d grease nipple, may be accessed by a grease gun with a hose, so that it is not necessary to be under the vehicle or trailer while performing the adjustment. Thus, it is possible to pump grease into the hydraulic adjuster from any desirable location, such as to the side of the vehicle.
In another preferred embodiment specifically, a mechanical adjuster comprises a housing, a pinion gear on a spring-loaded shaft, a gear rack, locking teeth, and a ram. The pinion shaft may be pushed in against the spring, freeing it from the locking gear, and allowing the shaft to be turned by conventional tools. Turning the pinion shaft drives the rack in or out of the housing. A slotted adjusting ram at one end of the rack straddles a saddle at one end of a brake shoe. Another slotted ram, fixed at the opposite end of the housing, straddles the end of the other shoe. As with the hydraulically powered embodiment, the adjuster is not fixed to the back plate, but is allowed to float. Thus, turning the pinion shaft can take up clearance between the shoes and the drum and the shoes will center themselves. Releasing pressure on the pinion shaft allows the spring to force the pinion gear into engagement with the locking teeth inside the housing, thereby fixing the proper adjustment.